1. Field of the Invention
The present invention relates to a method and device for controlling an automatic transmission.
2. Description of the Related Art
Generally, a control device is known that controls gear shifting of an automatic transmission by applying oil pressure to a plurality of frictional elements of the automatic transmission. In such automatic transmission control devices, if any anomaly occurs in an electromagnetic valve or pressure control valve that adjusts the oil pressure to be applied to the frictional elements, it becomes impossible to apply correct oil pressure to the frictional elements. To cope with such problem, decision as to whether gear shifting is permissive or not has been conducted by monitoring a nomalies by means of an oil pressure switch which electrically detects if the oil pressure applied to the frictional elements has reached a threshold value (see Japanese Patent Laid-Open Publication No. Hei 1-224549). If a threshold value is reached, a fail-safe valve is mechanically activated.
However, neither the oil pressure switch nor the fail-safe valve is activated unless oil pressure applied to the frictional elements reaches the threshold value. In some cases,however,it is more difficult than in normal cases to vary the oil pressure that is applied to the frictional elements to engage or release them for shifting to a target gear and in such cases it will take more time for the applied oil pressure to reach the threshold value. This means that it takes more time to detect an anomaly and hence to judge whether the gear shifting is permissive or not, and thus the gear shifting cannot be conducted rapidly.